How to Wire a Double 40 Amp Breaker for a Home A/C Unit

Wiring a double-pole, 40-amp circuit breaker for a central air conditioning system is something that any moderately skilled DIY electrician can accomplish without difficulty. Wiring a 2-pole circuit breaker for an air conditioning system requires working inside the service panel, where the main panel lugs will still be electrified even with the main service disconnect breaker turned off. The main lugs are the two terminals on the main service disconnect breaker. Depending on the make and model panel that you're working with, the main breaker may be located at the top or bottom centers of the panel or at the top or bottom, left- or right-hand side.

1

Turn off the main service disconnect breaker. Turn on the noncontact voltage tester and bring it near the cable leaving the service panel. The noncontact tester will beep continuously if there is still power going to the branch circuits and remain silent if the panel is safe to open and work in. If there is still power on the cable, you have turned off the wrong breaker. The proper breaker will be labeled "Main."

2

Remove the screws holding the panels outer and inner covers in place. As a rule, the outer panel cover will be held in place by six screws and the inner cover will be held in place by four screws. Set the covers to one side and replace the screws in the panel box for safe keeping. Once you have removed the covers, place a sheet of rubber or dry cardboard over the main panel lugs, so you don't accidentally make contact with them.

3

Install the new 2-pole, 40-ampere circuit breaker in the panel. Depending on the panel that you're working with, the breaker may simply snap into place on the bus bars, or it may be secured to the bus bars with screws.

4

Slide the cable through the cable connector on the side of the panel box and secure in place by tightening the two clamping screws on the connector. Remove the cable's outer insulating jacket with the razor knife, beginning 1/4 inch from where it exits the cable connector.

5

Route the red and the black insulated wires over to the circuit breaker. Cut off the excess wire to make a neat connection. Strip off 3/4 inches of insulation from the ends of the red and black wires. Slip the stripped ends under the terminals and then tighten the terminal screws to secure them in place.

6

Route the white neutral wire to the panel's neutral bar. Shorten the neutral wire as needed to make a neat connection. Strip its end and slip the stripped end through one of the empty holes on the silver neutral bar. Tighten the screw down on the wire.

7

Run the bare copper grounding wire down to the panel's ground bar, the silver-colored bar with the green-colored screws. Connect the ground wire to the grounding bar by slipping it in an empty hole and tightening the screw down on it.

8

Push all the wires into the panel safely away from the panel's opening. Replace the inner and outer panel covers. Turn the main service disconnect breaker back on.

Things You Will Need

Noncontact voltage tester

Flat-blade screwdriver

Rubber pad or piece of dry cardboard

2-pole, 40-ampere, 240-volt circuit breaker

Wire cutters

Utility knife

Wire strippers

Warning

Even though the main lugs are still electrified, everything else inside the panel will be safe with the main breaker turned off. This is a safe project because there is no reason for you to work anywhere near the two lugs/terminals. For an extra safety precaution, you can cover the lugs with a piece of rubber or dry cardboard.

About the Author

Based in Colorado Springs, Colo., Jerry Walch has been writing articles for the DIY market since 1974. His work has appeared in “Family Handyman” magazine, “Popular Science,” "Popular Mechanics," “Handy” and other publications. Walch spent 40 years working in the electrical trades and holds an Associate of Applied Science in applied electrical engineering technology from Alvin Junior College.

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